If someone masturbates will he become unholy, impure? If yes, how can he regain his purity?
There is a tradition reported from Imam Ja’far as-Sadiq (a.s.):
أَبُو عَلِيٍّ الْأَشْعَرِيُّ عَنْ عِيسَى بْنِ أَيُّوبَ عَنْ عَلِيِّ بْنِ مَهْزِيَارَ عَنِ الْقَاسِمِ بْنِ عُرْوَةَ عَنِ ابْنِ بُكَيْرٍ عَنْ زُرَارَةَ عَنْ أَبِي جَعْفَرٍ ع قَالَ قَالَ: مَا مِنْ عَبْدٍ إِلَّا وَ فِي قَلْبِهِ نُكْتَةٌ بَيْضَاءُ فَإِذَا أَذْنَبَ ذَنْباً خَرَجَ فِي النُّكْتَةِ نُكْتَةٌ سَوْدَاءُ فَإِنْ تَابَ ذَهَبَ ذَلِكَ السَّوَادُ وَ إِنْ تَمَادَى فِي الذُّنُوب زَادَ ذَلِكَ السَّوَادُ حَتَّى يُغَطِّيَ الْبَيَاضَ فَإِذَا غَطَّى الْبَيَاضَ لَمْ يَرْجِعْ صَاحِبُهُ إِلَى خَيْرٍ أَبَداً وَ هُوَ قَوْلُ اللَّهِ عَزَّ وَ جَلَّ- كَلَّا بَلْ رانَ عَلى قُلُوبِهِمْ ما كانُوا يَكْسِبُونَ
“There is no servant who does not have a white spot in his heart. When he commits a sin a black spot emerges from this spot. If he repents, the blackness goes away but if he insists on committing sins and continues doing so the blackness keeps on increasing till it covers up the whiteness of the heart completely. When the white spot is totally covered by the blackness, the owner of this heart will never go back to goodness. and this is the meaning of Allah's word:
“No indeed! Rather their hearts have been sullied by what they have been earning." (83:14)
In verse 53 of Surah Zomar we read:
قُلْ يا عِبادِيَ الَّذينَ أَسْرَفُوا عَلى أَنْفُسِهِمْ لا تَقْنَطُوا مِنْ رَحْمَةِ اللَّهِ إِنَّ اللَّهَ يَغْفِرُ الذُّنُوبَ جَميعاً إِنَّهُ هُوَ الْغَفُورُ الرَّحيمُ
Say] that Allah declares, [" O My servants who have committed excesses against their own souls, do not despair of the mercy of Allah. Indeed Allah will forgive all sins. Indeed He is the All-forgiving, the All-merciful.
The first step of repentance is to be sincerely sorry and regretful and make a conscious and strong decision not to commit sins again and in order for one to be able to take this step he has to deepen an understanding of the nature of the sins.
The second step is to make up for what he has done before. If he has violated others' rights he should compensate for them. If he has ignored Allah's rights, for instance, he has missed some obligatory prayers, he should decide to make up for them as soon as possible.
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Yes he does by indulging in such acts ipso facto as it constitutes zina of eyes and thoughts. However, its salvageable by seeking forgiveness from Allah.
"And Allah would turn to you in mercy; but those who follow vain desires would have you go tremendously astray"
"And who is further astray than he who follows his desire without guidance from Allah."
"And those who guard their chastity (i.e. private parts, from illegal sexual acts). Except from their wives or (the captives and slaves) that their right hands possess, - for them, they are free from blame. But whoever seeks beyond that, then those are the transgressors."
"And let those who find not the financial means for marriage keep themselves chaste, until Allah enriches them of His bounty."
From Abu Muhammad Hadith
None of you (truly) believes until his desire or inclination is in accordance with what I have brought or subservient to what I came with
From all those above Quaranic verses and one hadith its clear that to remain an ardent follower we have to abstain from all considered haram including masturbation.
Now to get back to being pristine, you will have to undo what harm has been done and guard yourself from repeating it. If you surrender yourself to the shade of Allah, you will not astray. To seek forgiveness recite "astagfirullah(I seek forgiveness from Allah)" at least 133 times with full heart after the act so done(Better if you make it a proclivity). Insha'Allah you will be forgotten.
To beat the temptation indulge in dhikr SubhanAllahi, al adheem, wa bihamdihi, SubhanAllahil azim (Glorified is Allah, The Supreme, Praised is he, Allah is free from imperfections) at least 100 times morning and evening besides salat. This will purify your thoughts, heart and shield your nafs from temptations invigorated by Satan.